Copper base alloys



Sept. 17, 1968 R. D. SMITH COPPER BASE ALLOYS Filed March l, 1966 QNIN @44444444444 Qmv f INVEN R. RICHARD DALE /T/'l v ATTORNEY United States Patent O Fice 3,402,043 CUPPER BASE ALLOYS Richard Dale Smith, Madison, Conn., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Mar. 1, 1966, Ser. No. 530,873 8 Claims. (Cl. 75-157.5)

The present application relates to new and improved copper base alloys. More particularly, the present invention resides in greatly improved copper base alloys containing zinc, laluminum [and cobalt, said alloys having greatly improved physical properties and being suitable for a wide range of applications, including castings, forgings, extrusions, and hot or cold rolled or drawn products. The improved alloys of the present invention are particularly suitable for use in wrought products.

Over the years, numerous attempts have been made to improve the strength characteristics of ductile brass without sacrifice of -formability. These attempts have concentrated on utilizing a great variety of alloying additions in order to achieve this goal. Some of these alloying additions are quite expensive and add considerably to the cost of the alloy.

In addition, the art has thoroughly explored many unusual thermo-mechanical processes in order to improve the strength characteristics without sacrificing for-mability.

The high strength brasses which have been developed in the art generally are multiphase -alloys having limited ductility and cold formability. Such alloys are most suitable for application as castings or hot worked products.

Despite these extensive investigations, 70/ 30 brass has prevailed over the years as the best and most economical copper base alloy for severe forming applications.

Accordingly, it is a principal object of the present invention to provide an improved copper base alloy.

It is an additional object of the present invention to provide a copper base alloy having improved strength levels in either the fully annealed or cold worked tempers.

It is an additional object of the present invention to provide improved copper base alloys as aforesaid which achieve improved strength characteristics with minimal sacrifice in formability.

It is an additional object of the present invention to provide an improved copper base alloy las aforesaid, said alloy being characterized by relatively low cost so that it is economically suitable on a large scale.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention, it has now been found that the foregoing objects may be readily and conveniently achieved. The improved alloy of the present invention consists essentially of the following ingredients in the following ranges, wherein all percentages are weight percentages: copper from 67 to 80%, zinc from 15.0 to 31%, aluminum from 1.0 to 5.0%, and cobalt from 0.1 to 3%.

It has been found that the foregoing alloy achieves greatly improved physical properties rwith minimal sacrifce in formability. For example, the improved alloy of the present invention has yield strength characteristics in the fully annealed condition on the order of 45,000

3,402,043 Patented Sept. 17, 1968 p.s.i. and over; whereas conventional copper base alloys for forming applications normally -achieve yield strengths in the fully annealed condition in the range of 10,000 to 25,000 p.s.i. and rarely over 30,000 p.s.i. The alloys of the present invention have correspondingly high yield strengths in the cold worked temper, for example, 90,000 p.s.i. and over after 50% cold reduction; whereas conventional alloys normally fall in the range of 50,000 to 75,000 p.s.i.

In addition, and importantly the alloys of the present invention are characterized by a high formability. Using the highly formable 30 brass as a standard, the alloys of the present invention have compara-ble formability. This is particularly surprising in view of the high strength of the alloys of the present invention.

These surprising characteristics in an inexpensive alloy are particularly unexpected in view of the extensive art in this field attempting -to approximate these characteristics.

The alloys of the present invention are known as modified aluminum-brasses and basically have either of the following structures: (1) an alpha (face-centered cubic) structure; or (2) an alpha plus a limited amount of beta (body-centered cubic) structure.

The addition of aluminum to copper-zinc alloys has long been known for its strengthening effect on such alloys. 'I'he disadvantage of the aluminum addition is that in saturated alpha phase alloys, which have highest strengths, small variation in aluminum content generally results in large variations in ductility and strength. These large variations are a result of the structure of the saturated alloy changing markedly with Ialuminum content. -For example a change in aluminum content of one percent may cause an increase in beta phase content of up to 33 percent.

In accordance with the present invention it has been surprisingly found that the addition of cobalt in the range of 0.1 to 3% by weight overcomes the disadvantages of the ternary copper-aluminum-zinc alloys such that properties and structure are more uniform over a practical range of aluminum content. In addition, a very marked grain refining effect occurs upon the addition of cobalt which is highly advantageous.

In accordance with the present invention the alloying ingredients must critically fall within the foregoing ranges. The copper content must fall within the range of 67 to by weight and preferabmly from 70 to 76% by weight. Below 67% by weight lthe strength falls ofi markedly and above 76% -by weight in saturated alloys an additional phase, termed gamma having a complex cubic crystal structure, may be encountered with slow cooling cycles which limits the ductility ,of the alloy.

Similarly, the zinc content is within the range of 15.0 to 31% by weight and preferably from 19 to 28%. The aluminum content should be maintained in the range from 1.0 to 5.0% by weight and preferably 2.0 to 4.5% and the cobalt content should be maintained in the range 0.1 to 3% and preferably 0.1 lto 1.0%.

For maximum ductility-formability at any given copperaluminum level, the cobalt content should be between 0,1 and 1.0% while for greater strength and lesser ductility the cobalt may approach higher levels up to 3%. Above this level of cobalt, little improvement in properties is realized since excess cobalt appears as elemental metal particles or as massive cobalt plus aluminum intermetallic compound and in addition, ductility decreases.

In general, the lower cobalt content alloys are high strength, high ductility materials; whereas the higher cobalt content alloys provide even higher strengths, but lower ductility.

The composition of specic alloys within the above ranges are subject to the further internal restriction that at about the 69% level of copper the aluminum content should preferably be in the range of 1.2 to 3.2% in order to insure high ductility-strength characteristics and at about the 74% level of copper the aluminum content should preferably be between 3.0 and 5.0% for the same reasons. Pfroportiona-te adjustments of aluminum content for the various copper contents between the specied limits should preferably be made.

Furthermore, in order to attain the preferred properties the aluminum content should preferably be related to the zinc content in accordance with the following equation:

Weight percent Al=-0.29 wt. percent Zn+9.2il.35

The subject alloys are represented in the attached drawings which are isothermal (932 E), constant cobalt (0.5%) sections of the quaternary phase diagram. FIG- URE 1 shows the relative location of the alloys of the present invention lon the ternary phase diagram. FIGURE 2 shows the shaded section of FIGURE l. In FIGURES l and 2 the solid line represents the alpha phase boundary. In FIGURE 2, the dotted line represents the alloys of the present invention at constant 0.5% cobalt. Similar diagrams may be readily constructed for other cobalt levels.

The structure of the alloys of the present invention in the cold worked and annealed condition is either (l) a matrix of fine grained, face-centered cubic, alpha phase (saturated or very nearly so), or (2) satura-ted alpha plus beta phase, with both structure (l) and structure (2) having very fine intermetallic compound ancl/ or precipitate particles dispersed throughout.

The alloys of the present invention may include in addition to the foregoing materials conventional impurities typically found in commercial copper base alloys. In addition, various other alloying ingredients may be added to achieve particularly desirable results. Common impurities may include: lead; tin; phosphorus; iron; manganese; nickel; and silicon. For minimizing dezincication in corrosive environments, the addition of arsenic, antimony and/or phosphorus may be desirable in an amount from 0.02 to 0.10%.

In general, the alloys of the present invention have an alpha plus particulate phase or an alpha plus beta plus particulate phase structure and are utilizable in a wide variety of applications. In view of their high strength and high formability, they are preferably provided in the wrought form. The oxidation resistance and castability of the alloys of the present inventionare excellent suggesting widespread application as high strength, low cost foundry alloys while their excellent hot forming properties also make them desirable for forgings as well as extrusions. In general, better combinations of mechanical properties at low costs are obtainable with the alloys of the present invention than are .available in any currently produced copper base alloys regardless of price.

Processing of the subject alloys requires no unusual treatment. As an example, the processing to sheet is as follows. Melting and casting are performed under similar conditions as brass alloys. Direct chill (DC) casting is particularly suitable. Hot rolling is easily accomplished using normal brass mill procedures. Under rapid cooling conditions a non-equilibrium structure may be obtained which reduces initial cold rollability. This may be overcome by an anneal in the range of 1000 to 1200 F. wherein prac- 4 tical equilibrium proportions of alpha and beta phases are attained.

It has been observed in the processing of the subject alloys that they exhibit an unusually high response to low temperature stress relief annealing following cold working. Normally, copper base alloys which have been heavily cold worked may respond with an increase in yield strength of -up to 15% when annealed at temperatures below the recrystallization temperature. This increase also normally is of practical consequence only with'in a relatively narrow range of annealing temperatures (50 to 100 F.). In the alloys of this invention, increases in yield strength of 30 to 40% have been noted upon low temperature annealing of lmaterial cold rolled 50%.`Further,`this response occurs over a wider range of temperature to 200 F. span), thereby increasing its commercial applicability. The magnitude of improvement in strength properties will be illustrated in the examples which form a part of the present specification.

Because of the stabilizing influence of cobalt on the structure, the properties of recrystallization annealed material are also stable over quite an extended temperature range. For example, the yield strength of a typical composition only decreased from 64,000 p.s.i. to 60,000 p.s.i. after one hour anneals at 700 F. and 1000 F. respectively. Tensile strength is similarly uniform While elongation steadily increases over the same range of temperature.

A further outstanding characteristic of the subject alloys is `a very marked improvement in stress corrosion resistance. The copper-zinc brasses are highly susceptible to stress corrosion cracking when exposed to certain corrosive environments. This susceptibility is proportional to zinc content and hence alloys containing more than 15% zinc are rarely chosen for stressed applica-tions in corrosive environments. It has been found that the cobalt modied aluminum brasses have greatly improved resistance to stress corrosion cracking when compared to the binary copper-zinc alloys. This behavior will be apparent from the ensuing examples. Coupled with this stress corrosion resistance is a high level of resistance to general corrosion.

The present invention will be more Ireadily understandable from a consideration of the following illustrative examples.

Example I Alloys having the compositions listed below were prepared from cathode copper, slab zinc, either cobalt metal, copper-cobalt master alloys, or aluminum-cobalt master alloy, and aluminum metal pellets. Preparation followed the ensuing sequence. Cathode copper chunks were melted under charcoal, .a portion or all of the desired aluminum content was added and stirred in, cobalt in the form of metal pellets, copper-15% cobalt master alloy or aluminum-30% cobalt master was added next and the melt was held .at temperature until complete solution occurred, zinc chunks were added and stirred in. The melt at a temperature of about 2000o F. was poured into a cast iron mold and allowed to solidify.

The resulting ingots were reheated to 1500 to l650 F. and hot rolled lfrom 1.750 to 0.300, iinishing at about 1000 F. Material was then cold rolled to 0.120, annealed at 1000 F. for one hour, cold rolled to 0.060", annealed at 1000 F. for one hour and cold rolled to 0.030". Material was evaluated in the final 50% cold rolled condition at 0.030" and also in the annealed condition where various temperatures were used.

For comparative purposes, commercial 70/ 30 brass and a copper-aluminum-zinc alloy were subjected to the same treatment, except that the 70/30 brass was interannealed at 800 F. instead of 1000? F.

The properties are given in the following table, i.e., yield strength at 0.1% offset, tensile strength and percent elongation both in the cold rolled an annealed tempers.

TABLE I 50% Cold Rolled 1,000 F. Anneal, 1 hr. 1,200" F. Anneal, 1 hr.

Alloy Composition Wt. percent Yield Tensile Percent Yield Tensile Percent Yield Tensile Percent Y Strength, Strength, Elonga- Strength, Strength, Elonga- Strength, Strength, Elotgap.s.i. p.s.i. tion p.s.i. p.s.i. tion p.s.i. p.s.i. tion 120, 000 2. 5 60, 000 87, 000 33 51, 500 83, 000 35 133, 500 2. 2 l 56, 000 33, 500 25. 2 115, 500 2 2 {1 43, 500 72,000 34. 5 126, 000 2 3 1 49, 500 39, 500 29. 5 84, 000 34. 5 130, 000 2.1 l 02, 500 s0, 500 20 127, 500 2. 0 L! 44, 500 76, 000 37. 5 83, 100 37. 6 114,000 2 0 27,000 65,000 57 2 41, 000 32, 000 29 VIII 70 Cu, 30 Zn 74, 500 90, 000 3 5 2 21,800 53,000 50 1 1,100" F. Anneal, 17 hour cycle, 3 hour hold. 2 800 F. 1 hr.

1. A copper base alloy consisting essentially of copper Example II from 67 to 80% by weight, zinc from 15.0 to 31% by T0 illuStrae the unusually high feSPOIlSe O 10W temweight, aluminum from 1.0 to 5.0% by weight, cobalt from perature annealing Alloy IV from Example I was sub- 0 1 to 3,0% by weight, jected to a one hour anneal at 400 F. with the following 2, An alloy according to Claim 1 wherein the alumiresults- 20 num and zinc contents are in accordance with the equa- TABLE II Tensile Properties 50% Cold Rolled, 0.1% oiset 50% Cold Rolled -l- Annealed 1 hr. at 400 F.

Yield Tensile Percent Yield Tensile Percent Strength, Strength, Elen- Strength, Strength, Elonp.s.i. p.s.i. gation p.s.i. p.s.i. gation Aney 1v 00,000 120,000 2.3 134,000 147,300 1.4

Example In tion: wt. percent Al=.-0.29 wt. percent 2n+0.2i l.35. 3. An alloy according to claim 2 wherein said zinc 1s Several of the alloys prepared in Example I were evalupresent in on amount from 19 to 28%, ated -OT fofmabitl/ Slug tW0 Common measurements, 4. An alloy according to claim 2 wherein said aluminum i.e., limiting draw ratio determination for evaluating deep 35 is present in nn amount from 2,0 to 45% by Weight, dfuWublY, and 015611 CUP testing t0 Check Stretch 'fofm 5. An alloy according to claim 2 wherein said cobalt is ability. These results show the improved alloys of the present in an amount from 0 1 to 1 0% present invention to be fully equivalent in drawability to 6, An alloy according to Claim 2 wherein Said copper 70/30 brass (listed for comparison and only slightly is present in an amount from 70 to 75% lCSS Ollllable in Stretch forming than 70/30 bIaSS. 40 7 An alloy according t() Claim 2 including a material selected from the group consisting of arsenic, antimony TABLE 1H and phosphorus in an amount from 0.02 to 0.10% by Alloy Limiting Draw Ratio Olsen Bulge Height Weight. a

2 276 0374 4r 8. An lmproved copper base alloy consisting essential- 2270 0.400 0 ly of copper from 70 to 76%, aluminum 2.0 to 4.5%,

2-260 0420" Zinc 19 to 28% and cobalt 0.1 to 1.0%, wherein the aluminum and zinc contents are in accordance with the This invention may be embodied in other forms or equation: wt. percent Al=-0.29 wt. percent Zn-i-9.2

carried out in other ways without departing `from the 50 1.35 spirit or essential characteristics thereof. The present em- Reierences Cited bodiment is therefore to be considered as in all respects FOREIGN PATENTS illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency areWihliniiselaimtel braced therem CHARLES N. LOVELL, Primary Examiner.

12,160 7/1963 Japan. 578,873 7/1946 Great Britain.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIGN Patent No. 3,402,043 September I7, 1968 Richard Dale Smith It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 50, "preferabmly" should read preferably Column 5, line 39, after "comparison" insert a closing parenthesis. Columns S and 6, TABLE I, the seventh and eighth columns should appear as shown below:

same table, heading to the last column thereof, "Percent Elotgation" should read Percent Elongaton Column 6, line 3l, wt. percent Al=0.29 wt. percent Zn+0.2il.35" should read wt. percent A1=-0.29 wt. percent Zn+9.2il.35

Signed and sealed this 17th day of February 1970.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

1. A COPPER BASE ALLOY CONSISTING ESSENTIALLY OF COPPER FROM 67 TO 80% BY WEIGHT, ZINC FROM 15.0 TO 31% BY WEIGHT ALUMINUM FROM 1.0 TO 5.0% BY WEIGHT COBALT FROM 0.1 TO 3.0% BY WEIGHT. 